Speed filter

ABSTRACT

The invention proposes a speed filter ( 11 ) for an internal combustion engine. The speed filter ( 11 ) comprises a calculation rule (BV(i)), which is used to eliminate a torsional vibration of the i th  order completely or partially. The dynamics as well as the robustness of the speed control loop are increased in this way.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the priority of German application 101 22517.2, filed May 9, 2001, which was filed as International ApplicationNo. PCT/EP02/04922, on May 4, 2002, the disclosure of which is expresslyincorporated by reference herein.

FIELD OF THE INVENTION

[0002] The invention relates to a speed filter for an internalcombustion engine whose speed is detected in the form of the toothtiming of a shaft. The tooth timing values are used to determine afiltered tooth timing value by means of a speed filter, corresponding tothe actual speed value.

BACKGROUND OF THE INVENTION

[0003] An internal combustion engine that is provided as a generatordrive is conventionally supplied to the end user without a clutch andgenerator. The clutch and the generator are only mounted at the endcustomer's location. In order to ensure a consistent rated frequency forpower supply into the network, the internal combustion engine isoperated in a speed control loop. This detects the speed of thecrankshaft as a controlled variable and compares it to a target enginespeed, i.e., the reference variable. The resulting control deviation isconverted by means of a speed regulator into a manipulated variable forthe internal combustion engine, for example, an injection quantity. Theproblem with such a control loop is that torsional oscillations, whichare superimposed on the controlled variable, can be reinforced by thespeed regulator. Particularly critical are the low-pass oscillationscaused by the internal combustion engine, for example, torsionalvibrations of the 0.5 and 1^(st) order. When starting the drive systemthe amplitudes of the torsional oscillations can become so large due toreinforcement by the speed regulator that a limit speed is exceeded, andthe internal combustion engine shuts off.

[0004] The instability problem is countered with a speed filter in thefeedback path of the speed control loop. We are familiar with such aspeed filter from EP 0 059 585 B1. There the tooth timing values of ashaft are detected by means of a working cycle of the internalcombustion engine. The working cycle includes two revolutions of thecrankshaft, corresponding to 720 degrees. These tooth timing values arethen used to calculate a filtered tooth timing value by forming anarithmetic mean. It is updated after every working cycle. This filteredtooth timing value corresponds to the actual speed value, which is thenused to regulate the internal combustion engine. The problem with this2-revolution filter, however, is that a stable behavior of the drivesystem produces a worsening of the load acceptance behavior.

SUMMARY OF THE INVENTION

[0005] To this extent, object of optimizing the speed filter is theobject of the invention.

[0006] This object is achieved with the features described herein.

[0007] In accordance with the invention, the speed filter includes acalculation rule with which the torsional vibration of the i^(th) orderis eliminated completely or at least in part. The torsional oscillationof the 0.5^(th) order, for example, is eliminated completely through acalculation rule that provides that the current tooth timing value isadded to the tooth timing value of one revolution earlier. Contrary tothe 2-revolution filter from the prior art, this results in theadvantage that the actual speed value is already available at an earliertime. Speed detection is thus quicker compared to the prior art. Inother words, the dynamics of the speed control loop are increasedwithout endangering the stable behavior of the drive system. In order tominimize the influence of manufacturing tolerances of the odometers, itis provided in accordance with the invention that the tooth timingvalues are recorded at a specifiable angle of the shaft. Another measurethat is provided is that the speed filter additionally includes acompensating member, further including a low pass filter and adifferential member, for calculation of the filtered tooth timing value.By combining the invention with other transfer functions, e.g., averagefilters, new frequency responses can be created. The invention thusoffers the overall advantage that the speed control loop is very robustwith respect to disturbances, for example, temperature and manufacturingtolerance of the clutch. It is noted that resonance frequency of thedrive system decreases at higher temperatures.

[0008] The disclosure herein includes:

[0009] A speed filter for an internal combustion engine whose speed isdetected in the form of tooth timing values of a shaft and where fromthe tooth timing values by means of a filter a filtered tooth timingvalue, corresponding to the actual speed value, is calculated,characterized in that the speed filter comprises a calculation rule(BV(i), i=0.5, 1, 1.5, . . . ) for the complete or partial eliminationof a torsional vibration of the i^(th) order and by means of thecalculation rule (BV(i)) the filtered tooth timing value (y(k), k=1,2,3. . . ) is determined (y(k)=f(BV(i))) by adding a current tooth timingvalue (U(k)) and earlier tooth timing values (U(k−(N/2)), U(k−(N/3)).

[0010] A speed filter as described above, characterized in that theearlier tooth timing values (U(k−(N/2)), U(k−(N/3)) are weighted throughevaluation factors (k1, k2, . . . ).

[0011] A speed filter as described above, characterized in that thefiltered tooth timing value (y(k)) additionally is determined by meansof a compensating member), wherein the input variable (y1(k)) of thecompensating member corresponds to the output variable of thecalculation rule (BV(i)).

[0012] A speed filter as described above, characterized in that thecompensating member includes at least one differential member andpreferably a low pass filter.

[0013] A speed filter as described above, characterized in that thetorsional vibration of the i^(th) order is completely eliminated bycalculating the filtered tooth timing value (y1(k)) from the currenttooth timing value (U(k)) and the tooth timing value 1/(2i) earlier bymeans of the calculation rule (BV(i)).

[0014] A speed filter as described above, characterized in that thecalculation rule (BV(i)) is implemented in the following form:

y1(k)=y1(k−1)+(1/F)[U(k)+k1 U(k−F)]

[0015] with

[0016] y1(k) current filtered tooth timing value

[0017] y1(k−1) filtered tooth timing value from 2/N revolutions earlier

[0018] N number of tooth timing values detected per working cycle

[0019] F N/(4i)

[0020] i order of the torsional vibration that is to be eliminated

[0021] U(k) current tooth timing value

[0022] U(k−F) tooth timing value 1/(2i) revolutions earlier

[0023] k1 evaluation factor; equal to one.

[0024] A speed filter as described above, characterized in that thetorsional vibration of the i^(th) order is partially eliminated bycalculating the filtered tooth timing value (y1(k)) by means of thefollowing calculation rule (BV(i)):

y1(k)=y1(k−1)+(1/F)[U/(k)+k1 U(k−F)+Σkj U(k−(N/(4i+(j−1))))]

[0025] with

[0026] y1(k) current filtered tooth timing value

[0027] y1(k−1) filtered tooth timing value from 2/N revolutions earlier

[0028] N number of tooth timing values detected per working cycle

[0029] F N/4i

[0030] i order of the torsional vibration that is to be eliminated

[0031] U(k) current tooth timing value

[0032] U(k−F) tooth timing value 1/(2i) revolutions earlier

[0033] k1 evaluation factor; k1<1

[0034] j control variable j from 2 to ∞

[0035] kj evaluation factors

[0036] A speed filter as described above, characterized in that the sumof the evaluation factors (k1, k2 . . . ) is set at one (k1+k2+ . . .=1).

[0037] A speed filter as described above, characterized in that thecurrent tooth timing value (U(k)) and the earlier tooth timing values(U(k−(N/2)), U(k−(N/3)), . . . ) are averaged over a specifiable angleof the shaft.

[0038] A speed filter as described above, characterized in that thespeed filter is combined with another filter, particularly a mean valuefilter.

[0039] A speed filter as described above, characterized in that theorder i of the torsional oscillation that is supposed to be eliminatedis set at a fixed value or is calculated through frequency analysis.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040]FIG. 1 Illustrates a block diagram

[0041]FIG. 2 Illustrates a speed-time diagram of a start process

[0042]FIG. 3 Illustrates a speed-time diagram

[0043]FIG. 4 Illustrates a block diagram of the filter

[0044]FIGS. 5, 7 Illustrate an amplitude-frequency diagram

[0045]FIGS. 6, 8 Illustrate a phase-frequency response-frequency diagram

DETAILED DESCRIPTION OF THE INVENTION

[0046]FIG. 1 depicts a block diagram of the control system of theinternal combustion engine 1 with coupled control loop structure.Represented are: a speed regulator 6, an engine torque regulator 7, aselecting device 8, an injection start regulator 9 and the internalcombustion engine 1 with the injection system, for example, a commonrail system. The internal combustion engine 1 drives an engine load 4,for example, a generator or a ship's propulsion, via the shaft 2. On theshaft 2 gear wheels 3 are arranged. The tooth timing values U(k) andV(k) of the gear wheels 3 are detected by the speed sensors 5. Thecurrent tooth timing value U(k) is used to calculate a filtered toothtiming value y(k) or accordingly an actual speed nMOT(ACTUAL) by meansof a speed filter 11. The engine torque MK on the output of the internalcombustion engine 1 is determined with the torque filter 10. The actualengine speed nMOT(ACTUAL) is used as an input variable for the speedregulator 6 and the injection start regulator 9 in this type of controlloop structure.

[0047] The input variables of the speed regulator 6 are: the actualengine speed nMOT(ACTUAL), a speed difference dnMOT and a signal ve2.The speed difference dnMOT is calculated from the actual engine speednMOT(ACTUAL) and a target engine speed nMOT(TARGET). The signal ve2corresponds to the output signal of the engine torque regulator 7. Theoutput variable of the speed regulator 6 is a signal ve1. This signal ispassed to the selecting device 8 and the engine torque regulator 7. Theinput variables of the engine torque regulator 7 are: the engine torqueMK, a differential torque dMK, the signal ve1 and a regulating mode RM.The differential torque dMK is calculated from the engine torque MK anda maximum permissible engine torque. The output signal of the enginetorque regulator 7 is the signal ve2. This signal is directed at theselecting device 8 and the speed regulator 6. The selecting device 8 isused to establish which of the two regulators 6 or 7 is dominant, forexample, by means of a minimum value selection of the two signals ve1and ve2. The output signals of the selecting device 8 are aperformance-determining signal ve and the regulating mode RM. Theperformance-determining signal ve is directed at the injection device ofthe internal combustion engine 1 and the injection start regulator 9.

[0048] By the performance-determining signal ve, the injection quantityor the control response of a control rod are to be understood.

[0049] The input variables of the injection start regulator 9 are: theactual engine speed nMOT(ACTUAL), the performance-determining signal vesupplied by the selecting device 8 and further input variables E, forexample, the maximum combustion pressure value. The output variable ofthe injection start regulator 9 is the start of injection SB, which ispassed on to the internal combustion engine 1. Since the interaction ofthe speed regulator 6 with the engine torque regulator 7 and theinjection start regulator 9 is not relevant for understanding theinvention, no additional details need to be provided.

[0050] The speed control loop includes, as shown in FIG. 1, of thefollowing components: speed regulator 6, the internal combustion engine1, speed sensors 5 for detecting the tooth timing values and a feedbackpath with the speed filter 11.

[0051]FIG. 2 shows a speed-time diagram for the start process of a driveunit, for example, an internal combustion engine with generator. Thedash-dotted line represents the reference variable for speed control,corresponding to the target speed nMOT(TARGET). The solid line is theactual speed nMOT(ACTUAL). At the time t1 the reference variable isincreased from a starting value n1 to the value n2 until time t2 in aramp-like manner. From time t2 on the reference variable remainsunchanged. The actual speed nMOT(ACTUAL) initially follows thisreference variable. From time t2 on, however the actual speednMOT(ACTUAL) exceeds the specified value n2. During the time t3 throught4, the actual speed nMOT(ACTUAL) of the internal combustion enginebegins to oscillate. The causes for these speed oscillations can be: animpermissibly high dispersion of the injectors, the failure of oneinjector and/or a defective coordination of the entire system. In thesetorsional vibrations, the 0.5^(th) order has proven to be particularlydominant. This is shown in FIG. 2 in a sectional view. In practice, theamplitudes in an internal combustion engine with an operatingtemperature in part become so great that a speed limit is exceeded andan emergency stop is triggered. This results in the actual speed curveafter the time t4.

[0052]FIG. 3 shows the curve of speed nMOT on the crankshaft over time.Two torsional vibrations, corresponding to the 0.5^(th) and 1^(st)orders during a working cycle, i.e. 720 degrees of the crankshaft of theinternal combustion engine are represented. In FIG. 3, 5 tooth timingvalues are shown in an exemplary fashion: U(k−N), U (k−(N−1)), U(k−N/2), U (k−N/4) and U(k). The parameter N here characterizes thenumber of tooth timing values detected per working cycle. U(k)designates the current tooth timing value. Tooth timing is the durationbetween a first impulse and a second impulse or between severalconsecutive impulses of the gear wheels 3. In practice the spacing anglebetween two teeth can be, e.g., 3 degrees. This means that a maximum of240 tooth timing values are detected for one working cycle of theinternal combustion engine. Typically, the tooth timing values arestored in a circular buffer.

[0053] It becomes apparent on the basis of FIG. 3 that with the additionof the current tooth timing value U(k) to the tooth timing value of onerevolution earlier U(k−N/2), the torsional vibration of the 0.5^(th)order can be eliminated. The torsional vibration of the 1^(st) order canbe eliminated completely by adding the current tooth timing value U(k)to the tooth timing value of a half revolution earlier U(k−N/4). Thecorresponding mathematical conversion into a calculation rule BV(i) forthe complete elimination of torsional oscillation of the i^(th) order isas follows:

y1(k)=y1(k−1)+(1/F)[(U(k)+k1 U(k−F)]

[0054] wherein

[0055] y1(k) current filtered tooth timing value

[0056] y1(k−1) filtered tooth timing value 2/N revolutions earlier

[0057] N number of tooth timing values detected per working cycle

[0058] F N/(4i)

[0059] i order of torsional vibration to be eliminated

[0060] U(k) current tooth timing value

[0061] U(k−F) tooth timing value 1/(2i) revolutions back

[0062] k1 evaluation factor, value equals one

[0063]FIG. 4 shows a block diagram of the speed filter 11. The inputvariables are the tooth timing values U(k). These tooth timing valuesU(k) correspond to the tooth timing values detected over 2/N crankshaftrevolutions. The output variable is a filtered tooth timing value y(k),alternatively the actual speed nMOT(ACTUAL). The tooth timing valuesU(k), U(k−(N/2)), etc., represent the input variable for a functionblock calculation rule BV(i), reference number 12. A tooth timing valuey1(k) is determined with calculation rule BV(I), which no longercontains the torsional vibration of the i^(th) order. Since due to theaddition of tooth timing values, the calculation rule BV(i) representsan unstable algorithm (integral behavior), the algorithm is stabilizedby adding a subsequent compensating member 15. The compensating member15 here includes at least one differential transfer member (D-member). Alow pass filter 14 can be arranged thereafter. Mathematically this meansthat the transfer functions of the calculation rule BV(i), of thedifferential member 13 and the low pass filter 14 are multiplied witheach other. The filtered tooth timing value y(k) represents the outputvariable of the compensating member 15. By means of the function block16, it is converted into the motor speed nMOT(ACTUAL).

[0064] The discrete transfer function G(z) of the speed filter can bedescribed as follows:

G(z)=y(z)/U(z)

[0065] wherein

z=e Exp(sTa)

[0066] Here the following applies:

[0067] Ta scanning time of the filter algorithm

[0068] y(z) z-transformed filtered tooth timing value y(k)

[0069] U(z) z-transformed unfiltered tooth timing value U(k)

[0070]FIGS. 5 and 6 represent both the amplitude-frequency response(FIG. 5) and the phase-frequency response (FIG. 6) of a first transferfunction G1 for the stationary engine speed 1500 RPM. A PT1 member witha time constant T1 of 5 msec was used as the low pass filter, and thetooth timing values were detected over a crankshaft angle of 90 degrees.One recognizes that the torsional vibration of 0.5^(th) order (12.5 Hz)has been eliminated completely.

[0071] In FIGS. 5 and 6, the amplitude and phase-frequency responses ofthe 2-revolution filter from the prior art are additionally depicted astransfer function G2. One can see that the transfer function G1 exhibitsthe considerably more favorable phase-frequency response, i.e., that the2-revolution filter has a considerably larger phase delay.

[0072] If the torsional vibration of 0.5^(th) order and the torsionalvibration of 1^(st) order are supposed to be eliminated partially, thecalculation rule BV(i) is executed as follows:

y1(k)=y1(k−1)+(1/(N/2))[U/(k)+k1 U(k−(N/2))+k2 U(k−(N/4)]

[0073] wherein

[0074] y1(k) current filtered tooth timing value

[0075] y1(k−1) filtered tooth timing value from 2/N revolutions earlier

[0076] N number of tooth timing values detected per working cycle

[0077] U(k) current tooth timing value

[0078] U(k−(N/2)) tooth timing value 1 revolution earlier

[0079] U(k−(N/4)) tooth timing value 0.5 revolution earlier

[0080] k1, k2 evaluation factors; k1+k2=1

[0081] Typical values are 0.8 for k1 and 0.2 for k2.

[0082] If again a filter of the 1^(st) order (PT1 member) with the timeconstant 5 msec is used in this example as the low pass filter and thetooth timing values are recorded over 90 degrees, it results in theamplitude and phase-frequency responses depicted in FIGS. 7 and 8(transfer function G3). One recognizes that the torsional oscillation ofthe 0.5^(th) order (12.5 Hz) is now no longer eliminated completely.Instead the torsional oscillation of the 1^(st) order is dampened morestrongly (25 Hz). A comparison of the phase-frequency responses oftransfer functions G1 and G3 shows that the transfer function G3exhibits a lesser phase angle rotation than the transfer function G1.

[0083] As represented, the invention makes it possible to filter outtorsional vibrations of any random order with less phase delay than withthe corresponding 2-revolution filter or mean value filter from thestate of the art. This leads to increased stability and better dynamicsof the speed control loop. Since the invention comprises tooth timingvalue detection over a specified angle, influences of manufacturingtolerances can be minimized. When the transfer functions of theinvention are combined with other transfer functions, e.g., mean valuefilters, new frequency responses can be created. The invention alsoallows additionally for any random number of tooth timing values in thepast to be included. The sum of the individual evaluation factors k1, k2. . . must equal 1, respectively.

[0084] In a drive system with soft clutches, this results in a low-passresonance frequency of the system. If the resonance frequency is in therange of the torsional vibration of the 0.5^(th) order, the speedcontrol loop can become unstable. However if the described speed filteris used, in the range of torsional oscillation of the 0.5^(th) order avery large dampening effect takes place, which has a stabilizing effectonto the overall control loop. The invention thus enables greaterrobustness of the speed control loop since most drive systems have aresonance frequency of less than 20 Hz. Greater robustness is achievedparticularly towards temperature influences since the resonancefrequency of the drive system becomes smaller at higher temperatures.Also with regard to manufacturing tolerances of the clutch (springconstant C, dampening) greater robustness is accomplished. In generalthe speed filter can always be used when point-symmetric periodicdisturbances are supposed to be eliminated and/or dampened.

[0085] The foregoing disclosure has been set forth merely to illustratethe invention and is not intended to be limiting. Since modifications ofthe disclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

1. Speed filter for an internal combustion engine (1) whose speed isdetected in the form of tooth timing values of a shaft and where fromthe tooth timing values by means of a filter a filtered tooth timingvalue, corresponding to the actual speed value, is calculated,characterized in that the speed filter (11) comprises a calculation rule(BV(i), i=0.5, 1, 1.5, . . . ) for the complete or partial eliminationof a torsional vibration of the i^(th) order and by means of thecalculation rule (BV(i)) the filtered tooth timing value (y(k), k=1,2,3. . . ) is determined (y(k)=f(BV(i))) by adding a current tooth timingvalue (U(k)) and earlier tooth timing values (U(k−(N/2)), U(k−(N/3)). 2.Speed filter (11) according to claim 1, characterized in that theearlier tooth timing values (U(k−(N/2)), U(k−(N/3)) are weighted throughevaluation factors (k1, k2, . . . ).
 3. Speed filter (11) according toclaim 1 and claim 2, characterized in that the filtered tooth timingvalue (y(k)) additionally is determined by means of a compensatingmember (15), wherein the input variable (y1(k)) of the compensatingmember (15) corresponds to the output variable of the calculation rule(BV(i)).
 4. Speed filter (11) according to claim 3, characterized inthat the compensating member (15) consists of at least one differentialmember (13) and preferably a low pass filter (14).
 5. Speed filter (11)according to claims 3 and 4, characterized in that the torsionalvibration of the i^(th) order is completely eliminated by calculatingthe filtered tooth timing value (y1(k)) from the current tooth timingvalue (U(k)) and the tooth timing value 1/(2i) earlier by means of thecalculation rule (BV(i)).
 6. Speed filter (11) according to claim 5,characterized in that the calculation rule (BV(i)) is implemented in thefollowing form: y1(k)=y1(k−1)+(1/F)[U(k)+k1 U(k−F)] with y1(k) currentfiltered tooth timing value y1(k−1) filtered tooth timing value from 2/Nrevolutions earlier N number of tooth timing values detected per workingcycle F N/(4i) i order of the torsional vibration that is to beeliminated U(k) current tooth timing value U(k−F) tooth timing value1/(2i) revolutions earlier k₁ evaluation factor; equal to one
 7. Speedfilter (11) according to claims 3 and 4, characterized in that thetorsional vibration of the i^(th) order is partially eliminated bycalculating the filtered tooth timing value (y1(k)) by means of thefollowing calculation rule (BV(i)). y1(k)=y1(k−1)+(1/F)[U/(k)+k1U(k−F)+Σkj U(k−(N/(4i+(j−1))))] with y1(k) current filtered tooth timingvalue y1(k−1) filtered tooth timing value from 2/N revolutions earlier Nnumber of tooth timing values detected per working cycle F N/4i i orderof the torsional vibration that is to be eliminated U(k) current toothtiming value U(k−F) tooth timing value 1/(2i) revolutions earlier k1evaluation factor; k1<1 control variable j from 2 to ∞ kj evaluationfactors
 8. Speed filter (11) according to claim 7, characterized in thatthe sum of the evaluation factors (k1, k2 . . . ) is set at one (k1+k2+. . . =1).
 9. Speed filter (11) according to claims 5 and 6 or 7 and 8,characterized in that the current tooth timing value (U(k)) and theearlier tooth timing values (U(k−(N/2)), U(k−(N/3)), . . . ) areaveraged over a specifiable angle of the shaft (2).
 10. Speed filter(11) according to one of the preceding claims, characterized in that thespeed filter (11) is combined with another filter, particularly a meanvalue filter.
 11. Speed filter (11) according to one of the precedingclaims, characterized in that the order i of the torsional oscillationthat is supposed to be eliminated is set at a fixed value or iscalculated through frequency analysis.